The present invention relates to a bracket mounting structure and a bracket mounting method for securely joining a bracket to an outer circumferential surface of a tube. Specifically, the present invention relates to a bracket mounting structure and a bracket mounting method which can be advantageously used for mounting a bracket on a cylinder of a fluid machine such as a piston-cylinder assembly, a hydraulic shock absorber, a gas spring, etc.
For example, a monotube type hydraulic shock absorber used in a suspension of a vehicle is configured such that a free piston is slidably accommodated in a cylinder (a tube) so as to define a gas chamber and an oil chamber in the cylinder, and a piston which divides the oil chamber into an upper chamber and a lower chamber is slidably accommodated in the cylinder. In such a monotube type hydraulic shock absorber, a support (a bracket) for supporting an external part such as a sensor or a hose is adapted to be mounted on an outer circumferential surface of the cylinder. To mount this support, a means of welding is conventionally employed. In this case, however, due to the effect of heat generated during welding, the cylinder is likely to be subject to strain or deformation. Therefore, a position at which the support is mounted is limited to a lower end portion of the tube, which is outside a slidable range of the free piston (see, for example, Japanese Patent Public Disclosure No. 2000-46090).
Recently, an attempt has been made to mount a spring seat or a knuckle bracket on a cylinder of a hydraulic shock absorber, by utilizing a technique called mechanical clinch, for the purpose of omitting welding (see, for example, Japanese Patent Public Disclosure No. 2004-223612). The mechanical clinch disclosed in Japanese Patent Public Disclosure No. 2004-223612 is a technique of pressing an overlapping part of an outer spring seat or knuckle bracket and an inner cylinder by means of a punch, to thereby deform both the spring seat or knuckle bracket and the cylinder locally in a radially inward direction, and thus fastening (staking) the spring seat or knuckle bracket to the cylinder. In this technique, however, a projection is formed in an inner surface of the cylinder as a result of the staking. Therefore, this technique cannot be applied to a cylinder such as that of the above-mentioned monotube type hydraulic shock absorber, in which an inner surface of a cylinder is used as a slide surface for a sliding member such as a piston.